How is it the wrong question to ask? What value judgement are you making? I'm curious because its hard to imagine any question being wrong(to ask) if its asked genuinely and without malice.
Why is that an insightful question? I wouldn't have expected a strong correlation, and from the article, there doesn't appear to be one.
At the risk of being too dismissive, I thought the reasons for linguistic diversity were already well known (that is, physical and political separation and a lack of trade/communication).